Riverton IA 05-NSH-1413

Assessment Comments

Assessment remains based on information from the IDNR Wildlife Bureau.

Basis for Assessment

[NOTE:  This wetland is not in the July 2003 version of the Iowa Water Quality Standards and is thus classified only for "general uses."  For the 2002 report, the waterbody identification number for this wetland was changed from "IA-WETLAND-21" to "IA 05-NSH-0015-L."]

SUMMARY:  The aquatic life uses are assessed (evaluated) as "fully supported” based on information from the IDNR Wildlife Bureau.   Due only to a change in IDNR's assessment/listing methodology, the 2004 assessment of the aquatic life uses ["fully supporting / threatened" (minor impacts)] is changed to "fully supporting".   Other than this change in methodology, this new (2006) assessment is the same as that developed for the previous (2004) assessment/listing cycle (not impaired) and does not reflect any known change in water quality.   Fish consumption uses remain "not assessed."   This is the same assessment as that develped for the 2002 reporting cycle.

EXPLANATION:  The aquatic life uses are assessed as "fully supported" based on information from the Iowa DNR Wildlife Bureau.   At the recommendation of U.S.  EPA Region 7, IDNR's 2006 assessment/listing methodology was changed to eliminate use of the "fully supported/threatened" (not impaired) category.   Thus, previous assessments identified as "fully supported/threatened" (not impaired) were changed to "fully supported" for the 2006 assessment/listing cycle.   This change does not alter the 2004 assessment:  this waterbody remains in IR Category 2a.

The level of support of the aquatic life uses in this wetland comples was upgraded from "partially supporting" (see assessments developed for the 1998 and 2000 reporting cycles) to "fully supported / threatened" for the 2002 assessment cycle.   This upgrade was based on the following information from the Iowa DNR Wildlife Bureau.   According to the local DNR Wildlife Biologist, Riverton normally has very good water quality but can receive considerable sedimentaion from extremely heavy local rains.   This wetland can also be inundated from high river flows in the East Nishnabotna and/or West Nishnabotna rivers when extremely heavy rains occur higher in their watersheds.   Based on this information, the previous identification of "siltation" as impairing the aquatic life uses of this wetland was potentially in error.   The assessment category for this wetland is "evaluated."  In terms of Section 305(b) reporting, "monitored assessments" are based primarily on recent, site-specific ambient monitoring data and thus have relatively high confidence.   "Evaluated assessments" are those based on data older than five years or other than site-specific ambient monitoring data (e.g., desktop models or questionnaire surveys of fish and game biologists [=best professional judgement]) and thus have relatively lower confidence.  

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this wetland.   In general, Iowa wetlands are not managed for recreational fisheries; thus, fish contaminant monitoring is not typically conducted at these waterbodies.